I have a 1990 Ford F150 truck with Fuel Injection. It's got the 5L engine.
For some reason, when the weather is cold, every so often I shut off the ignition switch, and I can hear the electric (in tank) fuel pump still running. Rotating the key will not stop it. The only thing that works is to restart the truck and shut it off again. This usually stops it. Or I can disconnect a battery cable.
What is causing this, and how do I fix it? The IGN switch shuts everything else off, so I doubt it's the switch itself, unless they have a separate contact just for the fuel pump.
Thanks